There are widely employed, as packaging materials for a variety of articles in the fields of foods, pharmaceuticals, electronic part items and the like, bag bodies each fitted with a plastic zipper. In particular, there are widely employed plastic zippers each equipped with a slider because of a ease in opening and closing and its capability of resealing.
FIG. 1 is a cross sectional end view showing a conventional plastic zipper the construction of which is such that a male hook M1-1 and female hooks F1-1 and F1-2 are engaged with each other so that the zipper is sealed. A slider which is usually employed for opening and closing the zipper is composed generally of an outside guide and an inside guide in such a structure that the inside guide which is inserted between the male hook and the female hooks slides so as to cause the male/female hooks to disengage, while the outside guide which sandwiches the male/female hooks therein slides so as to cause the male/female hooks to engage {refer to Japanese Patent Application Laid-Open No. 214920/1996 (Heisei 8)}.
However, with regard to the slider of the conventional structure, the inside guide is inserted between the hooks of a zipper, and even if the zipper is completely bound tight, the content in a bag leaks between the hooks and the inside guide which is inserted between the hooks. Hence, the above-mentioned conventional zipper is unusable for applications which require hermetical sealing and thus is used only for applications in no need of hermetical sealing such as general cargoes.
On the other hand, there is proposed a plastic zipper having such a structure that hermetical sealing can be maintained in a state of a engagement with a slider by the use of a specially shaped plastic zipper and a slider adapted thereto (for instance, U.S. Pat. Nos. 5,067,208 and 5,664,299). In regard to the plastic zippers as disclosed therein, hermetical sealability is maintained by taking advantage of the elasticity of the plastic material which constitutes the zipper for the purpose of facilitating the disengagement even with a weak force, and therefore when the elasticity thereof varies with a variation in temperature or the like, it is made impossible to maintain the hermetical sealability after opening and closing operations, whereby the amount of leakage is increased. Such being the case, the above-proposed zippers are unusable for packaging such content as liquid and the like in which occurrence of leakage is forbidden.
In the interim, there is proposed a zipper which comprising a pair of male hook/female hooks formed on a surface of a plastic film, a continuous tightening wall which is installed parallel to said male hook on the inside of said male hook and a continuous pressing rib which is installed parallel to said female hooks on the inside of said female hooks, whereby the zipper is imparted with excellent properties in persistent hermetical sealability and also impact resistance by the tight contact between the continuous tightening wall and the continuous pressing rib as well as self-tightening effect thereof (hereinafter referred to as “hermetically sealable zipper”) (Japanese Patent Registration No. 2,938,784).
FIG. 2 is a cross sectional end view showing the aforesaid hermetically sealable zipper in which the continuous tightening wall R 1 which is installed parallel to the male hooks M2-1, M2-2 on the inside of said male hooks and the continuous pressing rib which is installed parallel to the female hooks F2-1, F2-2 on the inside of said female hooks come in tight contact with each other and tighten the same. The above-mentioned hermetically sealable zipper, which is excellent in hermetical sealability and impact resistance and is almost free from performance variation due to temperature variation, is well suited for use in packaging liquid and the like.
The conventional slider with such constitution that the inside guide is inserted between the male hook and the female hooks, when used in the above-mentioned hermetically sealable zipper, impairs the much-awaited hermetical sealability. In such circumstance,. as a solution for this problem, the present inventor previously proposed a plastic zipper which is equipped with a slider and in which protrusions for slider guide are installed each parallel to a male hook and a female hook of a pair of male/female hooks in the opening side (outside) of the pair of male/female hooks for the plastic zipper, and the inside guide of the slider is positioned between the protrusions and the hooks in the opening side of the hooks therefor {Japanese Patent Application No. 316469/1999 (Heisei 11)}.
FIG. 3 is a cross sectional end view showing a plastic zipper equipped with protrusions for slider guide which is provided with protrusions G1-1, G1-2 each parallel to a male hook M2-1 and a female hook F2-1. FIG. 4 is a perspective view showing a slider to be employed for the zipper just mentioned. FIG. 5 is a cross sectional end view taken along the line B–B″ of FIG. 4 in which the slider S is composed of an inside guide S1 and an outside guide S2. FIG. 6 is a cross sectional end view showing a state in which the zipper is closed with a pair of male/female hooks that are sandwiched by the outside guide S2. FIG. 7 is a cross sectional end view showing a state in which the zipper is opened with the slider inside guide S1 positioned between the male hook M2-1 and the female hook F2-1 and the protrusions G1-1, G1-2. By the sliding of the slider equipped with the inside guide of the shape as illustrated on FIG. 5, the state of the slider is continuously changed from the state shown on FIG. 6 to the state shown on FIG. 7 via an intermediate state and vice versa, so that closing and opening of the zipper is carried out.
As a further improvement as illustrated on the perspective view of FIG. 8 in Japanese Patent Application No. 316469/1999 (Heisei 11), a proposal is made to ensure the closing of the zipper and tight contact of zipper parts by means of such constitution that a terminal portion of a plastic zipper for a bag body fitted with a plastic zipper is usually sealed on a heat seal portion HS, whereas there are provided, at a position immediately before the heat seal portion, hollows H1, H2 which are intended for stopping the inside guide and which penetrate between the top of the hooks F2-1, M2-1 on the opening side and the protrusions G1-1, G1-2 for slider guide.
Accompanying the diversification of objects to be packaged in recent years, higher hermetical sealability is required of the plastic zipper. At the same time, it is desired that the zipper be endowed with the function capable of detection of its having been unsealed after sealing packaging for the purpose of preventing unsealing thereafter due to an unfair purpose or mistake which brings about such disadvantages that foreign matters are mixed in the package and/or the quality of the content therein is impaired.
However, the above-mentioned plastic zipper equipped with a slider suffers from the disadvantage of its incapability of preventing unfair unsealing, since the zipper in a state of being closed can be opened by pulling from the outside, the protrusion portion for slider guide.